This invention broadly relates to digital video tape recording and, in particular, to a method and apparatus for recording and reproducing video signals as a function of copy information associated with those video signals.
Two countermeasures, namely automatic gain control (AGC) and color striping, have been generally used for assuring copy protection of a video signal on an analog videotape recorder (VTR). That is, disturbance signals, which disturb the automatic gain control function of the recording VTR, are inserted in the blanking period of television signals for copy protection in a conventional analog VTR. If a pre-recorded video tape is dubbed illegally, i.e. without authorization, the recording made on the dubbed tape becomes non-reproducible, thus assuring copy protection.
A processing known as color striping has also been proposed, wherein the phase of the color sub-carrier signal is inverted every 20 lines in the effective viewing area. Although a television receiver is not affected by such processing because of non-acute AFC control, the phase-locked loop of the AFC circuit in a VTR tends to follow such phase inversion closely, causing the reversal of the color phase to produce color bands.
These measures, however, are effective only for analog video signals. That is, in a digital VTR having no analog input and only a digital interface, the disturbance signal has no prohibitive effect on the recording even if copy protection exists. Thus, when the digital video signals are restored and outputted as analog signals, subsequent recording can be done on the VTR even though the original analog signals were copy-protected.